[Safari Larry]

This thread is for discussion of the Controlled Coupling (CC) Hydra-Matic transmission used by Pontiac 1956-64. The CC Hydra-Matic is sometimes called "dual coupling Hydramatic".

Pontiac changed over to the newly designed Controlled Coupling Hydra-Matic transmission in 1956. The CC transmission was used in the following:

Pontiac 1956-64 Strato-Flight, Super Hydramatic
Oldsmobile 1956-60 Jetaway
Cadillac 1956-64 Controlled Coupling Hydramatic
Hudson 1956-57 Flashaway
Nash 1956-57 Flashaway

In 1956 Pontiac used the controlled coupling "Strato-Flight" in all Star Chiefs except for the few that were equipped with standard transmission. 1956 Chieftains got the dual-range Hydra-Matic (aka "slant pan") -- unless special ordered with the extra cost Strato-Flight. For discussions on the dual-range transmission, see this thread.

The CC Hydra-Matic incorporated a secondary fluid coupling and a pair of sprag clutches in place of the dual range Hydra-Matic friction clutch and brake bands, shifting the front sun gear assembly by alternately draining and filling the secondary coupling. Essentially the secondary coupling acted as an internal fluid clutch. The transmission type for '56 can be easily identified by the shift indicator -- the dual range did not have a Park (P) position and the Strato-Flight did. See 1956 Hydra-Matic shop manuals:

1956 Hydramatic Manual - Part I Strato-Flight

1956 Hydramatic Manual - Part II Dual Range

The CC Hydra-Matic was smoother than the original Hydra-Matic and required less maintenance. However it was more complex and expensive to produce, as well as less efficient.

[U47]

Larry, can you explain how CC is less efficient? Power flow appears to be identical to Dual Range, so in top gear power flow to the driveshaft is the same and both units are locked just the same. Also this trans can be modified to hold shifts longer, and shift harder/faster. The only thing you can't do, just like in D Range is manually control first gear. I know that D Range was modified to shift 1, 1-2, 1-2-3, 1-2-3-4 by companies like B&M, I don't think anybody did that with CC 315 Hydramatic, however having raced with one, the hold on 1-2 really wasn't needed. With a 3.90 or 4.10 and a 3.97 first the gear was over in a flash even thought my car was modified for WOT 5,500 upshifts.

D.

[Safari Larry]

Don, let me first say I'm no expert on these transmissions. I know a little about them and worked of a few of them many years ago. I've studied the operating concepts and started this thread to learn more.

I picked up the comment that it was less efficient from the Wikipedia Hydramatic article. We already know that article has mis-information and maybe this is more of it. Here's the complete statement from that article:

With shifts taking longer and at higher engine speeds, however, performance and fuel efficiency suffered,compared to the original four-speed Hydra-matic.On the plus side, Jetaway was substantially smoother than the original Hydramatic, but also more complex and expensive to produce, as well as less efficient.

There are different aspects to efficiency and fuel efficiency is one -- and I can't comment on that. Regarding efficiency of transmitting power, it would seem (in theory) that the secondary coupling would contribute to some loss of efficiency. The secondary coupling is empty in first, filled going into second, emptied going into third and filled going into fourth. The secondary coupling replaces the front band in the dual-range. It would seem that filling and emptying the coupling would be less efficient and slower than applying/releasing a band. The secondary coupling would be a potential source for slippage but that might be insignificant, I don't know. Some slippage is desirable for a smooth shifting trans. I suspect the CC secondary coupling would would contribute to smoother shifting.

The Strato-Flight required an oil cooler, the dual-range did not (it was an option). That tells me the Strato-Flight was generating more heat. Heat is generated with power so that tells me more power is being lost to heat in the CC trans. Certainly filling/emptying the secondary fluid coupling along with the physical operation of the coupling would generate heat.

Don, you've had good results with the '59 CC trans but that doesn't mean it is intrinsically more or less efficient than the dual-range. It just means it was a good transmission. Your experience with the '59 is interesting.

[U47]

Larry, I believe the the manual says it takes four tenths of a second to fill or drain the coupling, and we (my dad) modified our 59 Catalina to drain and fill by 1/2 that time, plus a governor mod. and something else which I seem to have forgotten, anyroad after modifying that HD trans in 1959 we never touched that trans again with the exception of fluid changes (frequently) and linkage adjustment/checks. That was ten years of street, strip, and street racing and 96,000 miles. I should have never sold it. In the middle 60's I got my drag racing licence, regular drivers licence. At twelve, it was the car I learned to drive in.
Sure the trans caused more heat, but remember each year was a horsepower/torque and engine size change. After install big valve heads (after the second time water distribution tubes and two valve jobs) the car consistently ran 13.90's 101-102mph. Certainly there was a fuel efficiency change....I wonder if someone tested a 56 Chieftain vs. a Star Chief? Even so the Star Chief weighs more. Every year past that up until 1960 the cars gained weight so it's hard to compare.

[Safari Larry]

Four tenths of a second times three shifts = 1.2 seconds, very significant through the quarter mile for a stock trans. Cut that in half for 0.6 seconds through the quarter with your modified trans. I suspect that is in part the reason for using the dual range -- rather than the CC -- for modified high performance applications in the '60s. I'm sure there are other reasons.

Regarding the band of dual-range vs fluid coupling of the CC, an applied band is 100% efficient (no slippage when properly adjusted) and I suspect a fluid coupling is not. That could be another reason for preferring the dual-range for high performance.

From your experience, it would seem that reliability was not an issue with the CC trans -- and I've heard they were quite reliable in the later years of production. I think there were some issues with the early Turbo-Flights that made them less reliable. I recall (perhaps incorrectly) Steve Peluso (hydramatic Guru) has commented on that in the past. Perhaps he is "listening". Since I have the first year Strato-Flight, that is of interest to me.

Regarding fuel mileage, you might be right about comparing different models -- but the difference in weight of Chieftain vs Star Chief is only 70-80 lbs, comparing like models. The dual-range was heavier than the Strato-Flight. I can't comment on the validity of the better mileage claim (for dual-range) made by the Wikipedia article.

[U47]

Remember that the coupling controls the clutch and a one way sprag clutch is either 100% or it's not. I can tell you with 8.50 street tires on the rear the car would burn rubber all the way first, with no letting up-burn all the way through second gear, and chirp third gear even with our street 3.08 safety track.

Don

[Safari Larry]

For a good discussion on the Super Hydro, see this thead:

http://forums.maxperformanceinc.com/...d.php?t=541123

I haven't read it all yet but some good info there, including others who have good things to say about the Super Hydro.

Don, looking at the '56 manual "Fundamental Principles", it appears to me that the secondary coupling does not control the clutch or sprag. The coupling is full and transmitting power in second and fourth, the sprag and neutral clutch are effective only in first and third. The driven torus of the coupling is attached to the same shaft as the inner race of the sprag and to the overrun clutch plate but their effect is mutually exclusive, they don't work together. The shaft is either driven by the coupling or prevented from turning by the sprag/neutral clutch.

In second and forth gear, the front planetary unit is in direct drive. The secondary coupling ("front unit coupling") is full and transmitting power to the front unit sun gear (center gear) which results in direct drive of the unit. The sprag is released and the overrun clutch is off. The coupling transmits power to the front unit sun gear. The front unit ring gear (internal gear in Pontiac talk) is always driven by the engine through the torus cover, so the ring gear and sun gear are driven at the same speed if there is no slippage in the coupling -- which produces direct drive in the unit. If there is slippage in the coupling, the ring gear will turn faster than the sun gear and cause gear reduction. Power is output from the front planetary unit to the drive torus of the large main coupling. Slippage is possible in both fluid couplings in second and fourth gears. However in fourth gear, each fluid coupling transmits just 50% of power, 50% is mechanically transmitted through the ring gears.

That's the way I see it. However it's done, it seems to work well and the secondary coupling appears to be quite efficient. Results trump theory.

[U47]

Hi Larry, My 62 Pontiac Hydramatic ( Roto and Super ) has a very good description of mechanical, and hydraulic schematics. In the rear unit, the rear clutch, rear sprag clutch, neutral clutch are all controlled hydraulically. The front clutch is controlled hydraulically through the front unit coupling, which controls the front planetary gear set which is connected to and mechanically controls the front sprag clutch. It is also interesting to note that the drive ( large coupling ) coupling does the very same split torque advantage as the Dual Range HydraMatic.

[d2_willys]

The CC or DC hydramatic used the small coupling as the front clutch. The front sprag worked like the front band did on the early dual range units. The rear sprag took the place of the rear band, with only the rear clutch remaining from the early units. The overrun clutch, overrun band and neutral clutch were needed to hold the various planetary units while in DR3/S and Lo ranges. Those were not needed in the early units due to bands and clutches, not sprags and coupling. (If you look at a simple 3 speed Simpson gearset (C4, Torqueflite, etc.) transmission, you will see that 1st gear in DR range is accomplished by holding the rear planetary with sprag clutch, but when in LO, a rear band holds the rear planetary.)

As far as efficiency, I believe the actual gearsets are equally efficient. However the actual shifting times are much more pronounced with the early unit, than the "dump and fill" approach of the DC unit. Sprag clutches are weak links compared to bands and annular piston activated clutch paks. One plus that the DC had over the early dual range was the rear planetary ratio being higher in numeric ratio, thereby when the 2-3 shift was done, the rpm dropoff was much less severe. (Pontiac had done a similar change for the dual range units in 55 and 56)

Finally, the DC hydramatic had no band adjustments, so the maintenance on the unit was less.

[U47]

As far as efficiency, I believe the actual gearsets are equally efficient. However the actual shifting times are much more pronounced with the early unit, than the "dump and fill" approach of the DC unit. Sprag clutches are weak links compared to bands and annular piston activated clutch paks. One plus that the DC had over the early dual range was the rear planetary ratio being higher in numeric ratio, thereby when the 2-3 shift was done, the rpm dropoff was much less severe. (Pontiac had done a similar change for the dual range units in 55 and 56)

A interesting set of facts there, as mentioned by me before, the drain and fill time could be modified. I was wondering if the HD, Police and Taxi CC Hydramatic had different (heavier duty) sprag clutches, was also wondering while Roto does have a sprag clutch it also has a new similar clutch which appears to be better suited to stress called a roller clutch. Apparently after all the redesign of the dual range to Super Hydramatic to become more forgiving in shifting they introduce Roto which has the harshest 1-2 (2-3 range) shift ever because of Roto going into direct mechanical lock up with a drained coupling and a ratio jump from 2.93 to 1.56. That is quite a hurdle to get over and Supers 2.55 to 1.55 jump I thought was quite a stretch is a little better.
It's no wonder Chevrolet could never use any of those automatics in a passenger car. In their range of engines ( except the W engines) there was not enough torque to overcome those ratios. Imagine that trans behind a six. A P/U is another matter though where those drivers are used to a kick in the back.

D.

[Safari Larry]

Thanks d2, great explanation that helps considerably in understanding the differences and understanding how the CC trans works.

Don, not only does the main large coupling have the same power split torque as the dual-range -- but also it appears to me that the front unit with the small coupling has the 50/50 (mechanically driven/hydraulically driven) torque split when in direct drive (1:1), second and fourth gears. Of course, as usual, I could be wrong.

[d2_willys]

Originally Posted by U47

As far as efficiency, I believe the actual gearsets are equally efficient. However the actual shifting times are much more pronounced with the early unit, than the "dump and fill" approach of the DC unit. Sprag clutches are weak links compared to bands and annular piston activated clutch paks. One plus that the DC had over the early dual range was the rear planetary ratio being higher in numeric ratio, thereby when the 2-3 shift was done, the rpm dropoff was much less severe. (Pontiac had done a similar change for the dual range units in 55 and 56)

A interesting set of facts there, as mentioned by me before, the drain and fill time could be modified. I was wondering if the HD, Police and Taxi CC Hydramatic had different (heavier duty) sprag clutches, was also wondering while Roto does have a sprag clutch it also has a new similar clutch which appears to be better suited to stress called a roller clutch. Apparently after all the redesign of the dual range to Super Hydramatic to become more forgiving in shifting they introduce Roto which has the harshest 1-2 (2-3 range) shift ever because of Roto going into direct mechanical lock up with a drained coupling and a ratio jump from 2.93 to 1.56. That is quite a hurdle to get over and Supers 2.55 to 1.55 jump I thought was quite a stretch is a little better.
It's no wonder Chevrolet could never use any of those automatics in a passenger car. In their range of engines ( except the W engines) there was not enough torque to overcome those ratios. Imagine that trans behind a six. A P/U is another matter though where those drivers are used to a kick in the back.

D.

Chevrolet trucks used the hydramatic with 6 cylinders, and the 265 and 283 engines. Nash, Hudson, Kaiser, Willys, and Pontiac used the hydramatic with their 6 cylinder engines too. What they did was to put a numerically higher rear end ratio to overcome the rpm and torque dropoff at the 2-3 shifts. I have a Hudson super jet with hydramatic and that little car goes real well!

Now the DC and roto hydramatics were never used in Chevy and Buicks, but Hudson and Nash did use the DC hydramatic. The Roto was a very different transmission and not very reliable according to many people. The Oldsmobile F85's of the early 60's used the smaller roto 5 with the 215 aluminum V8. It had less torque than most V8's but the roto 5 seemed to work alright with that engine.

The early dual range hydramatics had an even bigger dropoff at the 2-3 shift due to the 2.63 to 1.45 ratio change. A 3.08 rear end ratio even with a 371 rocket had a hard time overcoming that drastic rpm dropoff. With a 3:70 Posi unit the dropoff was barely perceivable.

[Safari Larry]

Originally Posted by U47

I was wondering if the HD, Police and Taxi CC Hydramatic had different (heavier duty) sprag clutches...

Don, I looked up the rear sprag clutch (Group 4.180) in MPC. It is same for 1956-60 and there is no heavy duty. Couldn't find the front sprag.

[d2_willys]

Originally Posted by Safari Larry

Thanks d2, great explanation that helps considerably in understanding the differences and understanding how the CC trans works.

Don, not only does the main large coupling have the same power split torque as the dual-range -- but also it appears to me that the front unit with the small coupling has the 50/50 (mechanically driven/hydraulically driven) torque split when in direct drive (1:1), second and fourth gears. Of course, as usual, I could be wrong.

One thing I wanted to mention is that the front clutch of the early dual range units had to have less slippage than the small coupling will ever have.

[U47]

Originally Posted by d2_willys

One thing I wanted to mention is that the front clutch of the early dual range units had to have less slippage than the small coupling will ever have.

When the trans shifts from first to second, even while this is happening the slightest amount of pressure drop (in other words the coupling doesn't have to be completely empty) that front sprag will come off, this happens in fourth too. The rear sprag is not controlled by the front coupling as it gets it's signal from or through the neutral clutch. Third speed is a different story as the coupling controls the front sprag through the planetary gear set. Maybe engineers felt it could take it's time because of the large ratio jump to 3rd. All I know is I could chirp third gear with no problem with a set of 8.50's on the rear. Seemed pretty positive kicking to me, but as said before my trans was modified and what was modified is in the above thread as best I can remember.

Don

[d2_willys]

Originally Posted by U47

When the trans shifts from first to second, even while this is happening the slightest amount of pressure drop (in other words the coupling doesn't have to be completely empty) that front sprag will come off, this happens in fourth too. The rear sprag is not controlled by the front coupling as it gets it's signal from or through the neutral clutch. Third speed is a different story as the coupling controls the front sprag through the planetary gear set. Maybe engineers felt it could take it's time because of the large ratio jump to 3rd. All I know is I could chirp third gear with no problem with a set of 8.50's on the rear. Seemed pretty positive kicking to me, but as said before my trans was modified and what was modified is in the above thread as best I can remember.

Don

Don: Correct me if I am wrong, but front unit works like this:

First: Front sprag on, coupling empty (causes sprag to engage)
Second: Front sprag free-wheels due to coupling filled (only hydraulic control is coupling fill/dump, sprag controlled by coupling state)
Third: Same as first
Fourth: Same as second

If this is the case, then your last post is somewhat vague, and perhaps needs some refining.

In the case of the neutral clutch, I believe that is always on in DR-4, but is off in reverse and neutral. (I would have to look at the flow charts to list what it does in LO and DR-3.

In the case of 3rd and 4th gear, the sprag freewheels due to the rear clutch being engaged. The neutral clutch simply puts the sprag in an active state (Dr-4).

The DC and Roto hydramatics are very different to the dual range units. And IMO are way too complicated compared to the oldie! All GM had to do is to improve the 2-3 shifts and the oldie would have been just fine. Hell, Rolls Royce built it till 1967 and they must have thought it was good for those fine cars.

It seems that it took till 64 to use the Simpson 3 speed automatic gearset, that Ford, Chrysler, and imports thought was good, for GM to break down and pay the royalties for the Turbo 400 and it's successors. Instead GM told Hydramatic division to keep messing up the hydramatics till then. The Roto's were real beauts! And to think Buick was still messing with the Dynaflow, and Chevy used the Powerglides, it makes me think that GM was in a crisis mode from 56-64. (funny how Torqueflites were introduced in late 56!!!)

GM was also late in using common powertrain components too.

[U47]

D2-Willys, I'm afraid you will have to be more specific on the vague portion for me.
As far as complicated goes, they have a different way of clutching/de-clutching. The other thing I should mention, because of the split torque design all three Hydramatic's are the most efficient automatic's made until automatic's finally started to come with lock up converters. All three; Dual Range, Dual Coupling, and Roto are more efficient in high gear than a T-400, T350, or ST300, Powerglide or Dynaflow. The only company that did have a lock up was Packard's Ultramatic, but that transmission had it's problems along with not being very versatile being only a two speed.
I think I mentioned this maybe in dual range thread that Controlled Coupling final design was a compromise of the original design and concept. The original design called for three fluid couplings.
My understanding is that CC was designed to smooth the 1-2 shift, which they did a great job of doing. Many people don't even notice 1-2 at low-moderate speed and some people call it a three speed unknowingly. One of my buddies has a 47 and 48 Cadillac and his wife always complains of the 1-2 shift as it jerks her head off on that shift especially in a parking lot situation where you accelerate out of a parking stall and then lift the throttle to coast up to a street. I get a kick watching her head snap back when this happens, my buddy Jeff knows when it's going to shift, but she is oblivious until the lurch comes. One of the reasons the Rolls gets away with it is most likely the weight.
Controlled Coupling and Roto's biggest problem is the gear ratio selection. Even Dual range only had a ( I say only-that still very deep) a 3.82:1 first compared to a 3.97:1 of CC. If CC and Roto moved it up just a bit then the 2-3 shift in CC and the 1-2 shift in Roto would have made things much better.

As far as commonality goes in parts, GM found a way to build a very good set of transmissions to save money on each car, but by the time they started to do that with engines they realized they had gone too far. I remember the lawsuits that spun around GM when loyal Olds customers found Chevy engines in a car that was supposed to have a Rocket engine. Some of those people never bought a GM product after that happened. My dad bought a new 1950 Chieftain because he always had Pontiac's. His reasons were simple; Reliability, the only car in the low-mid price field to have tried and proven eight cylinder ( Olds V-8 was not proven yet in his mind and Chevy only came with a six ) Hydramatic drive, leaf springs and a open driveshaft (Chevy was still torque tube and Olds had coil springs in the rear--Pontiac had the best ride because it had the longest wheelbase of the three) . If you look at 1949-1952 GM bodies of Chevrolet, Pontiac, Olds ( Olds until 51 1/2 in 88's) they are basically the same form, and what separates them is their engines, transmissions, suspensions and rear ends and a little bit of wheelbase-Pontiac being the biggest by 5 inches on the Chevy and .5 on the Olds because of the straight eight. It was these differences that built customer loyalty and created a brand image. Later the Pontiac V-8 brought still more loyal people to Pontiac.

D.

[d2_willys]

Originally Posted by U47

D2-Willys, I'm afraid you will have to be more specific on the vague portion for me.
As far as complicated goes, they have a different way of clutching/de-clutching. The other thing I should mention, because of the split torque design all three Hydramatic's are the most efficient automatic's made until automatic's finally started to come with lock up converters. All three; Dual Range, Dual Coupling, and Roto are more efficient in high gear than a T-400, T350, or ST300, Powerglide or Dynaflow. The only company that did have a lock up was Packard's Ultramatic, but that transmission had it's problems along with not being very versatile being only a two speed.
I think I mentioned this maybe in dual range thread that Controlled Coupling final design was a compromise of the original design and concept. The original design called for three fluid couplings.
My understanding is that CC was designed to smooth the 1-2 shift, which they did a great job of doing. Many people don't even notice 1-2 at low-moderate speed and some people call it a three speed unknowingly. One of my buddies has a 47 and 48 Cadillac and his wife always complains of the 1-2 shift as it jerks her head off on that shift especially in a parking lot situation where you accelerate out of a parking stall and then lift the throttle to coast up to a street. I get a kick watching her head snap back when this happens, my buddy Jeff knows when it's going to shift, but she is oblivious until the lurch comes. One of the reasons the Rolls gets away with it is most likely the weight.
Controlled Coupling and Roto's biggest problem is the gear ratio selection. Even Dual range only had a ( I say only-that still very deep) a 3.82:1 first compared to a 3.97:1 of CC. If CC and Roto moved it up just a bit then the 2-3 shift in CC and the 1-2 shift in Roto would have made things much better.

As far as commonality goes in parts, GM found a way to build a very good set of transmissions to save money on each car, but by the time they started to do that with engines they realized they had gone too far. I remember the lawsuits that spun around GM when loyal Olds customers found Chevy engines in a car that was supposed to have a Rocket engine. Some of those people never bought a GM product after that happened. My dad bought a new 1950 Chieftain because he always had Pontiac's. His reasons were simple; Reliability, the only car in the low-mid price field to have tried and proven eight cylinder ( Olds V-8 was not proven yet in his mind and Chevy only came with a six ) Hydramatic drive, leaf springs and a open driveshaft (Chevy was still torque tube and Olds had coil springs in the rear--Pontiac had the best ride because it had the longest wheelbase of the three) . If you look at 1949-1952 GM bodies of Chevrolet, Pontiac, Olds ( Olds until 51 1/2 in 88's) they are basically the same form, and what separates them is their engines, transmissions, suspensions and rear ends and a little bit of wheelbase-Pontiac being the biggest by 5 inches on the Chevy and .5 on the Olds because of the straight eight. It was these differences that built customer loyalty and created a brand image. Later the Pontiac V-8 brought still more loyal people to Pontiac.

D.

Perhaps vague is not the appropriate word, but what I was confused about was the explanation about the front sprag operation with the front coupling. As I pointed out, it seems that your explanation was opposite to what I believe is correct.
The neutral clutch was also confusing as it is used to make the rear sprag active in conjuction with the rear clutch.

As far as the CC calming the 1-2 shift, I believe you are correct in stating that GM did this due to the abrupt 1-2 shift of the dual range. I, particularly have never had the abrupt shift in all my vehicles with dual range. The shift is very firm, but not jerky. My guess is that if the bands and TV pressure are not correct, the transmission will exhibit the abrupt shift. In 55-56 Pontiac moved the 1st gear ratio to 4.01 by changing the 1:45 ratio to 1:55. So, the dropoff of the 1-2 shift was even worse than the CC in those transmissions, but the 2-3 shift rpm dropoff was less severe.

Packard did have the lockup clutch, but so did Buick, with their dual path drive, used in 61-63 Specials and Skylarks. It was a pretty good little transmission, even though it was only 2 speeds. It had a unique way of providing reverse range. It used the same planetary as the lo range used.

[U47]

Don: Correct me if I am wrong, but front unit works like this:

First: Front sprag on, coupling empty (causes sprag to engage)
Second: Front sprag free-wheels due to coupling filled (only hydraulic control is coupling fill/dump, sprag controlled by coupling state)
Third: Same as first
Fourth: Same as second
-------------------------------------------------------------------------------------------------------------

Yes, the sprag clutch is controlled by the front coupling, but it's controlled indirectly. In other words the coupling controls the planetary gear set, and the gear set locks the sprag in first, or over runs it in second.

D.

[Safari Larry]

Originally Posted by U47

Don: Correct me if I am wrong, but front unit works like this:

First: Front sprag on, coupling empty (causes sprag to engage)
Second: Front sprag free-wheels due to coupling filled (only hydraulic control is coupling fill/dump, sprag controlled by coupling state)
Third: Same as first
Fourth: Same as second
-------------------------------------------------------------------------------------------------------------

Yes, the sprag clutch is controlled by the front coupling, but it's controlled indirectly. In other words the coupling controls the planetary gear set, and the gear set locks the sprag in first, or over runs it in second.

D.

To clarify... The only thing that controls the front sprag is direction of rotation of the shaft that the inner race is connected to (Front Coupling Driven Torus Shaft). The front sprag allows rotation of that shaft in one direction (direction of engine rotation) and locks the shaft from turning in the opposite direction. The sprag is a relatively simple unit directly controlled only by that shaft.

So Don's comment that the sprag is controlled indirectly by the front unit coupling seems correct because the filled coupling will cause the Front Coupling Driven Torus Shaft to turn in direction of engine rotation and will put the sprag in the off (not holding) condition and allow the shaft turn. The Front Coupling Driven Torus Shaft is also attached to the front unit sun gear so the sun gear is being turned in direction of engine rotation at engine speed, assuming the coupling is 100% efficient. In this condition, the ring gear and the sun gear are both turning turning at the same speed, in effect locking the ring gear to the sun gear. That causes direct drive of the front unit. This is where the division of power in the front unit comes into play. The ring gear is driven mechanically and the sun gear is driven through the front unit coupling with the same torque. That results in 50% power transfer mechanically and 50% power transfer though the front planetary unit.

When the front unit coupling is empty (not turning the shaft), then the front unit ring gear tries to turn sun gear (through the planetary gears) in opposite direction of engine rotation. Since the Sun gear is also attached to the Front Coupling Driven Torus Shaft then the sprag prevents the shaft from turning. With the shaft locked, the ring gear causes the planetary gears to "walk" around the sun gear. That puts the front unit in reduction.

Note that in fourth gear there are two power divisions (50/50 mechanical/coupling), in the front unit and in the rear unit. If power trasfer through a fluid coupling is considered to be less efficient that a mechanical connection, then I see this as a factor that would make the CC trans less efficient than the dual-range in fourth gear (in theory).

That's the way I see it.